1. Field of the Invention
The present invention relates to a solid electrolytic capacitor, and particularly, to an improvement in a terminal structure of a solid electrolytic capacitor capable of being surface-mounted on a circuit board.
2. Description of Related Art
A solid electrolytic capacitor having a structure shown in FIG. 11 has been conventionally known. A capacitor element 6 included in the solid electrolytic capacitor includes an anode element 3 made of a sintered body of a valve-action metal (tantalum, niobium, titanium, aluminum, etc.), a dielectric coating 4 made by oxidizing a surface layer of the anode element, and a cathode layer 5 having sequentially formed therein a solid electrolyte layer 5a made of a conductive inorganic material such as manganese dioxide or a conductive organic material such as TCNQ complex salt, a conductive polymer, etc. and a cathode lead layer 5b made of carbon, silver, etc. An anode lead frame 11 is connected to an anode lead member 7 planted on one end surface of the anode element 3, while a cathode lead frame 12 is connected to the cathode layer 5. A periphery of the capacitor element 6 is coated and sealed by an enclosure resin part 80 made of epoxy resin or the like. The anode lead frame 11 and the cathode lead frame 12 are bent along a surface of the enclosure resin part 80 (see JP 10-64761 A).
However, there has been a problem that the capacitor element 6 cannot be sufficiently large in overall size relative to a solid electrolytic capacitor finished product because the solid electrolytic capacitor of the above-described structure needs to have an entire periphery of the capacitor element 6 coated with an enclosure resin.
Accordingly, the present inventors have proposed a technique of incorporating a capacitor element 6 with a larger occupying volume relative to an overall size of a solid electrolytic capacitor finished product by mounting the capacitor element 6 on a platy anode terminal 10 and cathode terminal 20 as shown in FIG. 12 to make a gap as small as possible between an outer peripheral surface of the capacitor element 6 and an outer peripheral surface of an enclosure resin part 80 (JP 2001-244145 A).
In the solid electrolytic capacitor, an ESR (Equivalent Series Resistance) and an ESL (Equivalent Series Inductance) in the solid electrolytic capacitor finished product can be reduced because it is unnecessary to provide a lead frame bent along a surface of the enclosure resin part as conventionally, so that a current path from the capacitor element 6 to a circuit board can be shortened. Furthermore, a distance between current paths of an anode and a cathode to the circuit board can be shortened by extending the cathode terminal 20 of the solid electrolytic capacitor to the vicinity of the anode terminal 10 as shown in FIG. 13. An ESL in a high-frequency area can be thereby further reduced.
However, there has been a problem in the solid electrolytic capacitor shown in FIG. 12 and FIG. 13 that if a great external force acts on the anode terminal 10 and the cathode terminal 20 during manufacture or after completion, the anode terminal 10 and the cathode terminal 20 are likely to peel off from the enclosure resin part 80, and especially the cathode terminal 20 peels off easily.
There has been also a problem in the solid electrolytic capacitor shown in FIG. 12 and FIG. 13 that if moisture infiltrates from a bottom surface side of the enclosure resin part 80 into an interface between both the terminals 10, 20 and the enclosure resin part 80, because a distance from the bottom surface of the enclosure resin part 80 to the capacitor element 6 is short, the moisture easily reaches to the capacitor element 6 through a short path to thereby degrade characteristics of the capacitor element 6.